In the prior art, an n− polycrystalline silicon region and an n+ polycrystalline silicon region are formed on a major surface of a semiconductor substrate body in a way that the n− polycrystalline silicon region and an n+ polycrystalline silicon region make an intimate contact with each other. The semiconductor substrate body is obtained by forming an n− silicon carbide epitaxitial region on an n+ silicon carbide substrate. The epitaxitial region, the n− polycrystalline silicon region and the n+ polycrystalline silicon region form a hetero-junction among them. In addition, a gate electrode is formed adjacent to a junction part between the epitaxitial region and the n+ polycrystalline silicon region with a gate insulating film interposed between the gate electrode and the semiconductor substrate body. The n− polycrystalline silicon region is connected to a source electrode. A drain electrode is formed on the back surface of the n+ silicon carbide substrate.
A semiconductor device configured in the aforementioned manner functions as a switch, if electric potential of the gate electrode is controlled while the source electrode is being grounded and a predetermined positive electric potential is being applied to the drain electrode. In other words, a reverser bias is applied to the hetero-junction among the n− polycrystalline silicon region, the n+ polycrystalline silicon region and the epitaxitial region, while the gate electrode is being grounded. In addition, electric current dose not flow between the drain electrode and the source electrode. However, while the predetermined positive voltage is being applied to the gate electrode, a gate electric field works on a hetero-junction interface between the n+ polycrystalline silicon region and the epitaxitial region. This makes small a thickness of an energy barrier stemming from a hetero-junction surface of a gate oxidized film interface. For this reason, electric current flows between the drain electrode and the source electrode. In the prior art, the hetero-junction part is used as a channel for controlling shut-off and conductivity of the electric current. Accordingly, a channel length functions with a thickness of the hetero barrier. This makes it possible to obtain a conductivity characteristic with low resistance.